512 DR DAVY ON THE FREEZING OF THE EGG OF THE COMMON FOWL. 



nary conditions of incubation, taking the season of the year into account, the 

 habits of each kind of bird, and the kind of nest it forms. But whether it 

 belongs to the egg of the common fowl, to the extent which Mr Paget infers, 

 seems to me somewhat doubtful ; and also somewhat doubtful whether the 

 freezing of the egg is compatible with ani/ after development. In the following 

 passage the first is stated, the second is inferred. Speaking of the peculiar pro- 

 perty of the albumen, he says : — "The purpose or utility of this peculiar pro- 

 perty of the albumen of eggs is manifest in the defence which it provides 

 for the eggs exposed to a temperature below 32°. If an egg be frozen, the damage 

 sustained by its structure is such that the germ cannot be fully developed; 

 but mere cold, however intense, if freezing does not take place, does not 

 prevent the complete development of the young bird." In proof, he adds, " I 

 placed three eggs in a freezing mixture, varying from zero to 5° Fahr., one of 

 them froze, and its shell was cracked from end to end ; another froze, and 

 when it thawed, its yolk was burst and mixed with the albumen. In incuba- 

 tion, two spots of blood were developed in the former, and an enlargement of the 

 cicatricula ensued in the latter of these eggs — sufficient indications that the 

 intense cold and freezing had not killed them, though it had spoiled their struc- 

 ture.* But in the third egg, which had been exposed for nearly an hour to a 

 temperature below 5° Fahr., perfect development took place in incubation. 

 Even this degree of cold had neither killed nor frozen the egg, though, according 

 to the average rate at which eggs part with heat, its whole substance must have 

 been for half an hour at a temperature between 5 and 10" Fahr.'' 



These, it must be acknowledged, are very remarkable results, especially the 

 last. But, it may be asked, is it certain that in the two eggs, in which incipient 

 development was found to have taken place after apparent freezing, the yolk 

 was frozen, or that the part of it containing the cicatricula was structurally 

 damaged ? Moreover, is it certain that there was no mistake as to the egg 

 which was hatched after having been exposed to so a low a temperature? The 

 results which I have described, show how uncertain is the temperature at which 

 the freezing of the several parts begins. One experiment in such a matter, 

 when the result is anomalous, is hardly to be relied on. The experience of the 

 breeders of poultry is not in favour of eggs bearing any considerable degree of 

 cold with impunity. It is well known to them that the tendency of eggs to 



* Are, it may be asked, tlie above indications sufficient i In two instances I have found specks 

 of blood on the membrane of the yolk of the newly laid egg. In that of the last, I examined the 

 blood, and found it to contain well formed, elliptical nucleated corpuscles similar to those of the 

 adult fowl ; the inference made was, that the blood was derived from the oviduct in the descent of 

 the yolk. As to the enlargements of the cicati'icula, its evidence seems less open to objection ; and 

 yet, without a large comparison, can it be said with certainty, that the size was the result of increase 

 from development l 1 have found the cicatricula of a newly laid egg that had been fi'ozen, ap- 

 parently a little enlarged. 



